An initiative to give new fathers extra time at home with their babies was under attack last night after it was revealed that by the government's own estimates only 4% of men may take up the offer.

Family campaigners said the admission showed that government attempts to address work-life balance were being undermined and were no longer a priority.

In theory, 239,000 new fathers can take advantage of the move to spend up to six months on paternity leave. But figures drawn up by the Department of Trade and Industry show ministers expect only 10,000 men will benefit, because many are not entitled to leave or cannot afford to take more than the statutory two weeks around the birth.

Campaigners are warning that the scheme, under which mothers will have the option of letting their partner take the second six months of their maternity leave, provided that they return to work themselves, will not fulfil government promises of greater choice for families on care for children.

Those fathers whose partners do not work or do not return to work after having a baby will not be eligible to take the additional paternity leave.

Campaigners say thousands more fathers will not be able to afford to swap their salary for leave paid at the statutory rate of just over £100 a week - well below the minimum wage. Duncan Fisher, of the fatherhood pressure group Fathers Direct, said DTI forecasts of takeup of 4% to 8% of eligible fathers should be set against a 90%-plus takeup of paternity rights in other European countries.

The pressure group favours a "daddy month" approach used in Scandinavia, in which fathers are entitled to their own baby leave, cannot transfer it to their partner, and lose it if they do not use it.

Employers, already wary of the bureaucracy involved in sharing maternity leave between parents, would oppose a daddy month scheme. Susan Anderson, CBI director of human resources policy, said: "There is no appetite among employers for further extension of these rights."

Campaigners believe that, despite the latest consultation, the government has lost momentum over paternity leave reforms, and may not introduce them as promised by the end of this parliament, when maternity leave is also due to extend from nine months to a year.

The DTI consultation states that the earliest the changes could happen is April 2009, but adds: "This is not a firm date for introduction."

Concerns about the extent and pace of change for new fathers are being raised as the latest statistics suggest early progress towards flexible working for fathers may already be stalling in some jobs.

New DTI figures reveal that a quarter of men working in the private sector who asked to work flexibly had their requests refused, compared with only one in 10 women. Almost a fifth of men in public sector jobs have had requests turned down.

The DTI's flexible working review, slipped out on the department's website, reveals that the vast majority of workplaces - 93% - now offer some form of flexible working, a trend the DTI notes as "a cultural shift".

However, men are far less likely than women to take advantage of the change: 14% of eligible fathers asked to work flexibly last year, compared with 22% of mothers.

Case study: 'My 4-day week is more efficient'

When Chris Ainslie's three sons were born, he was able to take just one week's paternity leave with the older two (now 10 and nine) and two weeks with the youngest, now three.

Would he have taken more time off work to be with the babies and his wife, Stephanie, if the law had allowed it? "Absolutely," he says. "A week is not a long time for a baby, especially the first one, because then you have no idea what is going on and they do hugely change your life. I felt conscious that Stef was left with a baby without a great deal of support."

Mr Ainslie, 39, a vice-president of sales for BT global services, may not have been able to spend much time with Callum, Jordan and Harrison in their early weeks, but he has aimed to catch up since with a pioneering working arrangement he hopes will be seen as an example available to other fathers trying to balance work and family life.

Joining BT from Energis 18 months ago, he insisted he work a 40-hour week compressed into four 10-hour days, leaving Fridays free to spend with his wife and children, as well as pursuing his enthusiasm for sports and completing household chores in order to leave weekends free for family activities.

His decision to change his working life sprang partly from a personal tragedy: his identical twin brother's death prompted him to reevaluate his 80-hour-week work routine and give his family greater priority.

Despite initial scepticism in some quarters at BT, Mr Ainslie argues his spectacular business results and high satisfaction ratings from the 700 staff he manages make their own case. His four-day week, he says, makes for greater than usual organisation and efficiency - the last 18 months, he says, have been the most effective of his working life.

As well as achieving a better-balanced personal life, he is now a keen evangeliser for more options for working fathers, including those at senior levels.